1. Field of the Invention
The present invention relates to a photo film cassette. More particularly, the present invention relates to a photo film cassette of a type in which rotation of a spool advances a leader of photo film to the outside, and which includes improved flanges of the spool.
2. Description Related to the Prior Art
There are various documents U.S. Pat. No. 5,296,887, JP-A 2-18545 (corresponding to U.S. Pat. No. 4,848,693) and JP-A 4-320258 (corresponding to U.S. Ser. No. 655,944) which suggest a photo film cassette in which a cassette shell consists of molded parts of resin, and rotation of a spool core causes a leader of photo film to advance to the outside of the cassette shell. U.S. Pat. No. 5,083,155 (corresponding to JP-A 3-179341) suggests a container for containing developed photo film, the container including the cassette shell of the same structure for the purpose of facilitating handling and preservation of the developed photo film.
The photo film cassette includes a pair of flanges, which are disposed on respective axial ends of the spool core. There are circumferential lips formed on the respective periphery of the spool flanges to transmit rotation of the spool core reliably to the roll of the photo film. The circumferential lips partially wrap lateral edges of the outermost turn of the photo film to prevent the photo film from being loosened. In the course of advance and rewinding of the photo film, rigidity of the photo film causes the spool flanges to flex. Therefore the circumferential lips squeeze the lateral edges of the photo film between them.
In the course of advance of the photo film, the spool flanges must be spread by the photo film in the vicinity of the photo film passageway, in order to release the photo film from being partially wrapped by the circumferential lips. The spool flanges rotate always with deformation, and thus are originally formed with a small thickness. On the other hand, the spool flanges require sufficient rigidity, resistance to abrasion and other conditioned characteristics. Typically the circumferential lips must have considerable rigidity and resistance to abrasion for the reason of frictional contact with the lateral edges of the photo film in the course of the advance and rewinding of the photo film.
To provide the spool flanges with sufficient rigidity and resistance to abrasion, appropriate material for forming the spool flanges should be selected. Also an appropriate molding method for the spool flanges must be used. For example, documents such as U.S. Pat. No. 5,211,348 (corresponding to JP-A 4-251841), JP-A 6-148808 and U.S. Ser.No. 531,966 (corresponding to JP-A 8-146562) suggest a flange forming method. A polyethylene resin sheet is formed by extrusion with a thickness of 0.3 mm, and then heated and softened. Flange-shaped portions are formed by vacuum forming or pressure sure forming of the resin sheet, and then punched to obtain the spool flanges.
No matter whether good the material is to be used for the spool flanges in view of the rigidity and resistance to abrasion, the edge of the circumferential lips of the spool flanges of the prior art, having a rounded shape, still contacts the lateral edges of the photo film frictionally at one point. There remains possibility in rubbing the circumferential lips to create scraped powder or dust.
When the scraped powder or dust is created inside a camera, it is likely to be stuck on the photo film in exposure regions to lower photographic quality. The photo film according to the IX 240 type (Advanced Photo System, trade mark) is also provided with magnetic recording layer. The scraped powder or dust in the camera is likely to deposit on a magnetic head to cause failure in properly writing data to, or reading data from, the magnetic recording layer.